Thin film transistor liquid crystal display (TFT-LCD) has the advantages of small size, low energy consumption, no radiation, etc. As the size of the TFT-LCD increases and resolution improves, a drive circuit of higher frequency is used to improve the display quality, which leads to a more severe image signal delay of large size, high resolution TFT-LCD. The delay of the TFT-LCD signal is mainly decided by T=RC, wherein R is the signal resistance and C is the relative capacitance. Nowadays, the gate electrode, the gate electrode scanning line and data wire of the TFT-LCD are usually made by using metals such as Ta, Cr, Mo, etc. or the alloys thereof having stable chemical properties and high resistivity as the material of metal electrode. With the size and resolution of TFT-LCD increasing, the length of the gate electrode scanning line also increases, and the signal delay time also increases. Once the signal delay increases to certain level, some pixels will be inadequately charged, which leads to unevenness in the brightness, decrease in the contrast of the TFT-LCD, and affects the image display quality greatly.
As the size of the liquid crystal display increases, the frequency of the drive circuit also has to be increased. The mobility of the amorphous-silicon TFT(thin film transistor) is about 0.5 cm2/V·S. However, when the size of the liquid crystal display exceeds 80 inch and the drive frequency is 120 Hz, a mobility of no less than 1 cm2/V·S is necessary.
Metal oxide TFT (amorphous IGZO) is large in mobility, good in evenness, transparent and simple in manufacture process, can meet the requirement of the large size liquid crystal display and organic active electroluminescence and meet the requirement of large size, high refresh frequency LCD and OLED for high mobility. When metal Cu is used to form the drain electrode and the source electrode of TFT, Cu diffuses to the semiconductor layer, the gate insulating layer and the semiconductor protecting layer, which will affect the performance of TFT greatly. Therefore, before depositing the metal Cu thin film, barrier layer has to be deposited first.
The prior art has the following problems: when using amorphous IGZO to make TFT, a barrier layer is usually formed on the amorphous IGZO (semiconductor layer) to avoid that the amorphous IGZO is damaged when forming the Cu source electrode and drain electrode. However, this will add another patterning process, and when wet-etching metal Cu, since the etching rate of the metal Cu and that of the barrier layer are of great difference, the barrier layer will remain a bit after being etched and other thin films deposited thereupon will be badness in covering.